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Technology - Hardware

Bearing Basics

ABEC Rating

The ABEC scale is an industry standard for the tolerance of dimensions developed by the Annular Bearing Engineering Committee (ABEC) of the American Bearing Manufacturers Associations. There are five classes from looser to tighter tolerances: 1, 3, 5, 7 and 9. The tolerances mainly deal with the fit of the bearing with other components such as shafts and gears.

Higher ABEC ratings indicate tighter tolerances and higher precision. High precision and small tolerances are required for bearings to function at very high RPMs as found in products like high speed routers that spin at 30,000 RPM and above. In these applications, an ABEC - 7 or 9 bearing may be appropriate. A skateboard with 72mm wheels turning 20,000 RPM will be traveling more than 160 MPH! Since virtually all skating is done at less than 40 MPH, the realistic maximum RPM your skate bearings will see is about 6000 RPM. Probably 90% of skating occurs under 2000 RPM. Thus, very high precision is not required for skateboarding.

The ABEC classification does not specify many other factors that are important to skateboarding such as radial load strength, smoothness of rolling and rolling torque. Higher rated bearings are intended for precision applications like aircraft instruments and surgical equipment. Lower grades are intended for mechanical assemblies like vehicles and industrial machinery.

Bearing Numbering

Bearings are defined by a standard numbering system. The first number is the Type Code which indicates the type of bearing. All skate bearings are Single-Row Deep Groove Ball Bearings and are designated as a type “6” and are the most common. Examples of other types of bearings are “4” Double-Row Ball Bearing and “2” Spherical Roller Bearing.

The next number is the Series number which refers to the robustness of the bearing. The numbers and series that it indicates are listed below.

  • 8 – Extra thin section
  • 9 – Very thin section (Used in 10mm skate bearings)
  • 0 – Extra light (Used in 8mm skate bearings)
  • 1 – Extra light thrust
  • 2 – Light
  • 2 – Medium
  • 4 – Heavy

The next one or two numbers indicate the bore size. The bore size defines the inside diameter, outside diameter and width of the bearing and these values are different for each bearing Series. In skating, a bore size of “8” is used on 8mm skateboard axles. And a bore size code of “00” is used on 10mm axles.

These numbers are followed by codes that define special features such as the type of cover over the balls. A bearing without rubber seals or metal shields on both sides will quickly collect dirt, become slow, and need maintenance. Common codes are:

  • Z - Single shield
  • ZZ - Double shields (both sides)
  • RS - Single rubber seal
  • 2RS - Double rubber seals
  • V - Single non-contact seal
  • VV - Non-contact seals on both sides

The cover protects the bearing balls from contamination. Any debris falling into the bearing will slow it and reduce its life. Some skateboard companies only place a cover on one side since the other is inside the wheel core with the spacer. This is not recommended since this is not a clean environment and your bearings will not last. Seals are common and protect the balls well but they gently touch the balls and add friction. Shields do not touch the balls but, while protecting well, do not seal the bearing. Less common are non-contact seals. Other planet typically uses “ZZ” bearings with metal shields on both sides.

The sizes of the two bearings used in skateboarding are shown below. Note that 10mm axles bearing are 1mm narrower which does not matter and another reason to use spacers. Click here for more Click here for more bearing notes.

Bearing Axle ID OD Width
608-ZZ 8mm 8mm 22mm 7mm
6900-ZZ 10mm 10mm 22mm 6mm

BEARING MANUFACTURE and ASSEMBLY

                

Lubrication

Bearing lubrication is critical to performance and long life. Without proper lubrication bearing will over heat causing material damage and warping. This will slow bearings and may cause them to seize or fail completely. Two common lubricants are grease and oil. Grease is typically used for long life and lower costs. Grease is designed to be pasty at room temperature but melt into a liquid when in use. After use the bearing cools and the oil turns back to grease. This holds the lubricant in place for extended periods often eliminating the need for maintenance. When cool the grease is thick and more force is required to turn the bearing. In skateboards this means that the wheel will not spin as freely while holding your board. At speed when the grease has turned to oil friction is comparable to oil lubed bearings. Oil does not need to heat up for wheels to spin freely. Oil does not stay in place and will leak out over time.

In industrial applications oil lubricated bearing usually require a system to continually supply them with oil. Many skateboarders prefer oil lubed bearing for the free spin but must frequently re-oil to prevent wear and bearing damage. Some racers will use dry bearings with no lubrication. These bearings can be very fast when new but will have a very limited life. PTFE spray lubricants are favored by some skaters because they bond well to the bearing steel and are easy to apply. This type of lubricant is fine for skate bearings. Skating is not a specialist application so many lubricants will do a perfectly good job as long as you avoid the thick, high viscosity ones. Just don't be fooled by the finger spinning test.

A cheap bearing with no lubricant will spin much more freely than a good quality greased-steel bearing in the "finger test" but the cheap bearing rings are not as round and the raceways (grooves) are not as smooth. With higher speeds and higher loads, the cheap bearing has much higher vibration levels which cause much more drag than a low torque greased quality bearing. That is why the "finger test" is very misleading.

While bearings can be cleaned and reused they never will perform as well as a new one. If the bearing ball and races are damaged, cleaning will not fix it. In fact we believe that a new standard ABEC 1 greased bearing will outperform the best ABEC 7 oiled or dry bearing that is dirty or incompletely cleaned. REMEMBER - dirt in the bearing usually means damage to the surface of the balls and raceways. Cleaning is unlikely to restore the bearing to its original state. Best policy is to routinely replace your bearings.

Ceramic Balls Ceramic is sometimes used instead of steel for the balls in the bearing. Ceramic is ultra-hard, smooth and expensive as compared to steel. They are typically used because they resist damage, increase life and allow for higher speeds. Skateboarders sometimes opt for ceramic bearings because they are smoother rolling and have lower resistance to rolling. Are they worth the extra cost? The answer is different for everyone. The following video is a good overview of the critical elements to consider when choosing your bearings. Ceramic balls are discussed towards the end.

Other Planet's Offering

For our standard bearing Other Planet has selected ABEC1 greased bearings with double shields. These bearings offer the best value and longest life and should be ideal for most skateboarders. They should need no maintenance. We price them so that they can be replaced periodically at low cost. Don’t clean, replace. We recommend that bearings be changed often even if you do not use your board often. Bearings are steel and will corrode even without use.

Spacer Basics

Spacers have one basic and essential function. They prevent the wheel core from being crushed and deformed when tightening the wheel axle nut. The spacer fits inside the wheel core between the two bearings. When the nut is tightened the bearings and spacer are squeezed against the inside of the axle. Without a spacer the bearings are easily squeezed smaller than the plastic wheel core. This results in uneven compression, deforms the wheel and causes unbalance, increased friction and a slower ride. Without a spacer the core can also flex and loosen the axle nut. Riding without spacers is unsafe.

The size of the spacer is also important. The inside diameter should be large enough so as to fit freely on the axle. The outside diameter should not be bigger than that OD of the inner bearing race so that it does not drag on the balls as the bearings turn. Finally, the length must not be shorter the distance between the bearing seats of the wheel core. If it is shorter the core will still be squeezed. Wheels core are typically 0.400”, but since the cores are molded plastic this dimension varies. Many spacers are cut to 0.400” and also vary in length. This means that many spacers are too short for the wheels they are used in. Ideal spacers are about 0.402" - 0.405" preventing squeeze without getting too long.

Hardware Basics

Truck Mount Screws

Standard deck mounting hardware is size #10 with 32 threads per inch machine screws, commonly referred to as 10-32. (Note that another common size is 10-24 and that the nuts are not interchangeable since they have a coarser thread pattern.) Lengths vary depending on the deck, truck and other items such as pads and wedges. 1" and 1-1/4" lengths will work with most Other Planet truck set ups.

The head can have either a button head or be beveled for a flush fit and accommodate a standard screw driver a Phillips screw driver or a 1/8” Allen or hex wrench. We use hex button heads because we feel that countersinking a deck for a flush screw mount weakens the deck.

Screws come in steel, stainless steel, zinc plated and black oxide coated. We use black oxide coated hardware because of its corrosion resistance and what we feel is its superior appearance.

Nuts

All the nuts used in skateboard setups are typically of the nylon insert type. These nuts include a ring of nylon that deforms by the threads of the screw or bolt. This locks the nut onto the bolt and resists loosening from vibration. We use low profile nuts, which are shorter, for our axle nuts mainly because we feel they look better and give more flexibility in the use of spacers and washers.

Nylon insert nuts are designed for single use. Once the nylon is deformed the holding power decreases with each use. Skateboarding is not as demanding an application as aviation for which these nuts were developed, so they can safely be used a few times. They should however be replaced as often as possible to avoid the risk of loose nuts.

Helpful Facts

Nut Size Wrench Size Recommneded Troque (ft-lbs)
8mm Axle 5/16"-24 1/2" 20
10mm Axle 3/8"-24 9/16" 30
Deck Mount Screws 10-32 5/16" 3